Fluid pumps, whether driven by an internal combustion engine, an electric motor or by fluid system valves, have pressure fluctuations or pulses in the associated fluid line in the form of a fluid ripple. The fluid ripple undesirably generates audible and objectionable noise within the fluid pump itself and may also excite components downstream of the fluid pump (e.g., the steering gear in power steering systems), further increasing unwanted noise generation. Apart from the noise itself, the existence of a fluid ripple reduces the operational efficiency of the fluid pump. The pressure fluctuations are generated by pistons, gerotors, gears, vanes or other fluid displacement elements within the fluid pump, and at a frequency that is typically dependent upon the pump speed.
Tuning cables are used in the known art to attenuate fluid ripple frequencies in power steering systems. The power steering tuning cables are typically formed from wrapped steel or thermoplastic elements. However, both materials have their drawbacks. For example, in the case of wrapped steel cables, while inexpensive to manufacture, metal particles may cling to the wrapped steel tuning cables, eventually damaging the pump and valves, and reducing the performance of the tuning cable. Thermoplastic tuning cables are costly to manufacture.
In determining the optimal material for use in manufacturing power steering tuning cables, three main physical characteristics of the materials are considered. The ultimate or tensile strength, the elongation and the modulus (stress over strain) of materials are analyzed. Based upon these characteristics, the physical characteristics of Teflon® have made it a suitable material for use in the high temperature and extreme chemical environment associated with power steering tuning cables. Other materials, including cross-linked thermoplastic materials, are known in the art and have been used for power steering hoses, but have not been utilized to manufacture tuning cables due to the superior performance of Teflon®. However, as stated above, Teflon® is a costly material.